U.S. patent application number 09/992856 was filed with the patent office on 2002-10-10 for grease compositions for a hard disk drive and a process for production thereof.
Invention is credited to Mori, Shigeru, Okamoto, Yoshihisa, Shimizu, Sumio, Yamada, Tatsumi.
Application Number | 20020147119 09/992856 |
Document ID | / |
Family ID | 18813465 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020147119 |
Kind Code |
A1 |
Shimizu, Sumio ; et
al. |
October 10, 2002 |
Grease compositions for a hard disk drive and a process for
production thereof
Abstract
To provide a grease composition for HDD which is excellent in
low outgas generation and acoustic properties and a process for
production thereof. In a grease composition used in the bearing for
a hard disk drive, a basal oil comprising a paraffin-base
hydrocarbon and a polyurea as a thickener are contained.
Inventors: |
Shimizu, Sumio; (Chiba-shi,
JP) ; Yamada, Tatsumi; (Chiba-shi, JP) ; Mori,
Shigeru; (Kyoto-shi, JP) ; Okamoto, Yoshihisa;
(Tokyo, JP) |
Correspondence
Address: |
ADAMS & WILKS
ATTORNEYS AND COUNSELORS AT LAW
31st FLOOR
50 BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
18813465 |
Appl. No.: |
09/992856 |
Filed: |
November 5, 2001 |
Current U.S.
Class: |
508/552 |
Current CPC
Class: |
C10M 2205/06 20130101;
C10N 2040/42 20200501; C10M 2203/02 20130101; C10N 2020/01
20200501; F16C 2370/12 20130101; C10M 2203/022 20130101; C10M
2203/045 20130101; F16C 33/6633 20130101; C10M 2217/044 20130101;
C10M 105/04 20130101; C10M 169/04 20130101; C10N 2040/44 20200501;
C10M 2203/04 20130101; C10M 2205/0285 20130101; C10M 2217/045
20130101; C10N 2040/32 20130101; C10N 2040/36 20130101; C10N
2040/00 20130101; C10M 169/00 20130101; C10M 119/24 20130101; C10N
2040/30 20130101; C10N 2040/34 20130101; C10M 2205/028 20130101;
C10M 107/10 20130101; C10M 143/12 20130101; C10M 2203/024 20130101;
C10N 2040/50 20200501; C10N 2040/38 20200501; C10N 2040/40
20200501 |
Class at
Publication: |
508/552 |
International
Class: |
C10M 115/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2000 |
JP |
2000-338220 |
Claims
What is claimed is:
1. A grease composition for a hard disk drive which comprises a
basal oil comprising a paraffin-base hydrocarbon and a polyurea as
a thickener, which is used in the bearing for the hard disk
drive.
2. A grease composition for a hard disk drive according to claim 1,
wherein the paraffin-base hydrocarbon comprises a polyolefin
represented by the following general formula:H--[R.sub.1].sub.n
--H(wherein R.sub.1, is a saturated hydrocarbon group of which the
carbon number is 8-12; and n is a real number of 3-5) alone or as a
mixture of the olefins as a main component.
3. A grease composition for a hard disk drive according to claim 1,
wherein the paraffin-base hydrocarbon comprises components of which
the carbon number is 30 or more as main components.
4. A grease composition for a hard disk drive according to claim 3,
wherein the paraffin-base hydrocarbon comprises components from
which volatile components of which the carbon number is less than
30 have been eliminated in advance.
5. A grease composition for a hard disk drive according to claim 3,
wherein the content of the volatile components of which the carbon
number is less than 30 is 30 ppm or less.
6. A grease composition for a hard disk drive according to claim 1,
wherein the polyurea is formed by reacting a polyisocyanate readily
soluble in the paraffin-base hydrocarbon with a primary or
secondary (poly)amine in the paraffin-base hydrocarbon.
7. A grease composition for a hard disk drive according to claim 6,
wherein the polyisocyante is an aliphatic isocyanate.
8. A grease composition for a hard disk drive according to claim 6,
wherein the (poly)amine has a molecular weight of 400 or less.
9. A grease composition for a hard disk drive according to claim 6,
wherein the residual amount of the starting material contained in
the polyurea is 30 ppm or less.
10. A grease composition for a hard disk drive according to claim
1, wherein the polyurea is contained as particles of 1 ma or less
in average size.
11. A process for producing a grease composition used in the
bearing for a hard disk drive, which comprises a step for producing
a polyurea as a thickener by adding a polyisocyanate readily
soluble in a paraffin-base hydrocarbon and a primary or secondary
(poly)amine into a basal oil comprising the paraffin-base
hydrocarbon.
12. A process for producing a grease composition for a hard disk
drive according to claim 1 wherein the paraffin-base hydrocarbon
comprises a polyolefin of the following general formula: (wherein
R.sub.1 is a saturated hydrocarbon group of which the carbon number
is 8-12; and n is a real number of 3-5) alone or a mixture of the
polyolefins as main components.
13. A process for producing a grease composition for a hard disk
drive according to claim 11, wherein the polyisocyante is an
aliphatic isocyanate.
14. A process for producing a grease composition for a hard disk
drive according to claim 11, wherein the (poly)amine has a
molecular weight of 400 or less.
15. A process for producing a grease composition for a hard disk
drive as described in claim 11, which comprises a step for treating
at least the basal oil under reduced pressure.
16. A process for producing a grease composition for a hard disk
drive as described in claim 11, which comprises a step of adding an
excess amount of the (poly)amine to the polyisocyanate and
eliminating the residual (poly)amine after the reaction.
17. A process for producing a grease composition for a hard disk
drive according to claim 11, wherein the residual amount of the
starting material is 30 ppm or less.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to grease compositions used
for a hard disk drive and a process for production thereof.
[0003] 2. Description of the Related Art
[0004] FIG. 1 shows a structure of cross section of the hitherto
conventional hard disk drive (also referred to as an HDD). As seen
from the accompanying figure, magnetic disk 1 is fixed on the axis
4 of rotation in a freely rotatable state through the rotor 3 of DC
motor 2, wherein axis 4 is hold by ball bearing 5. Pivot assembly
10 that is attached to magnetic disk 1 to read and record the
magnetic data is equipped with swing arm 12 which has a magnetic
head 11 at the tip. Swing arm 12 is fixed on shaft 14 in a freely
swinging state through ball bearing 13.
[0005] For such ball bearings 5 and 13, grease is used, for which
is usually required a lubricating property, particularly a
long-term acoustic property. In recent years, however, also
required is reduction of the level of outgas generated under
operating conditions. That is, it becomes the most important
problem to reduce the outgas increasing with the use of a
large-capacity HDD or small-size HDD, increase of reliability and
accuracy, etc. Accordingly, the reduction of outgas generation is
highly necessitated, so as to be at a much lower gas level than in
the conventional grease.
[0006] As the conventionally used grease, thickened grease prepared
by adding an isocyanate compound and an amine to a basal oil for a
reaction to yield a diurea is known (e.g., Japanese Patent
Publication No. (herein after referred to as JP-B) 39-3114, JP-B
53-9243). Such grease, however, cannot be used for HDD because of
the high level of outgas.
[0007] On the other hand, Japanese Unexamined Patent Publication
No.11-325086/99 discloses low outgas grease prepared by adding a
lithium soap-type thickener to a basal oil comprising an aromatic
ester alone or an oily mixture of an aromatic ester and a polyol
ester. This official gazette also discloses the diurea-thickened
grease added to the basal oil as an example for comparison. This,
however, seems inappropriate to use for HDD in view of its acoustic
property and outgas.
[0008] However, it was found that such low outgas grease has no
performance required of grease for recent high performance HDD.
[0009] In view of the above circumstances, the object of the
present invention is to provide a grease composition for BDD, which
is excellent in low outgas generation and acoustic property, and a
method for production thereof.
SUMMARY OF THE INVENTION
[0010] The first embodiment of the invention for solving the
above-mentioned problems is to provide a grease composition for a
hard disk drive which comprises a basal oil comprising a
paraffin-base hydrocarbon and a polyurea as a thickener, which is
used in the bearing for the hard disk drive.
[0011] The second embodiment of the invention is to provide a
grease composition for a hard disk drive as described in the first
embodiment, wherein the paraffin hydrocarbon comprises a polyolefin
represented by the following general formula:
H--[R.sub.1 ].sub.n--H
[0012] (wherein R.sub.1 is a saturated hydrocarbon group of which
the carbon number is 8-12; and n is a real number of 3-5) alone or
as a mixture of the olefins as a main component
[0013] The third embodiment of the invention is to provide a grease
composition for a hard disk drive as described in the first and
second embodiments, wherein the paraffin-base hydrocarbon comprises
components of which the carbon number is 30 or more as main
components.
[0014] The fourth embodiment of the invention is to provide a
grease composition for a hard disk drive as described in the third
embodiments, wherein the paraffin-base hydrocarbon comprises
components from which volatile components of which the carbon
number is less than 30 have been eliminated in advance.
[0015] The fifth embodiment of the invention is to provide a grease
composition for a hard disk drive as described in the third and
fourth embodiments, where in the content of the volatile components
of which the carbon number is less than 30 is 30 ppm or less.
[0016] The sixth embodiment of the invention is to provide a grease
composition for a hard disk drive as described in any of the first
to fifth embodiments, wherein the polyurea is formed by reacting a
polyisocyanate readily soluble in the paraffin-base hydrocarbon
with a primary or secondary (poly)amine in the paraffin-base
hydrocarbon.
[0017] The seventh embodiment of the invention is to provide a
grease composition for a hard disk drive as described in the sixth
embodiment, wherein the polyisocyante is an aliphatic
isocyanate.
[0018] The eighth embodiment of the invention is to provide a
grease composition for a hard disk drive as described in the sixth
or seventh embodiment, wherein the (poly)amine has a molecular
weight of 400 or less.
[0019] The ninth embodiment of the invention is to provide a grease
composition for a hard disk drive as described in any of the sixth
to eighth embodiment, wherein the residual amount of the starting
material contained in the polyurea is 30 ppm or less.
[0020] The tenth embodiment of the invention is to provide a grease
composition for a hard disk drive as described in any of the first
to eighth embodiment, wherein the polyurea is contained as
particles of 1 or less in average size.
[0021] The 11th embodiment of the invention is to provide a process
for producing a grease composition used in the bearing for a hard
disk drive, which comprises a step for producing a polyurea as a
thickener by adding a polyisocyanate readily soluble in a
paraffin-base hydrocarbon and a primary or secondary (poly)amine
into a basal oil comprising the paraffin-base hydrocarbon.
[0022] The 12th embodiment of the invention is to provide a process
for producing a grease composition for a hard disk drive as
described in the 11th embodiment, wherein the paraffin-base
hydrocarbon comprises a polyolefin of the above-described general
formula alone or a mixture of the polyolefins as main
components.
[0023] The 13th embodiment of the invention is to provide a process
for producing a grease composition for a hard disk drive as
described in the 11th or 12th embodiment, wherein the
polyisocyanate is an aliphatic isocyanate.
[0024] The 14th embodiment of the invention is to provide a process
for producing a grease composition for a hard disk drive as
described in any of the 11th to 13th embodiment, wherein the
(poly)amine has a molecular weight of 400 or less.
[0025] The 15th embodiment of the invention is to provide a process
for producing a grease composition for a hard disk drive as
described in any of the 11th to 14th embodiment, which comprises a
step for treating at least the basal oil under reduced
pressure.
[0026] The 16th embodiment of the invention is to provide a process
for producing a grease composition for a hard disk drive as
described in any of the 11th to 15th embodiment, which comprises a
step of adding an excess amount of the (poly)amine to the
polyisocyanate and eliminating the residual (poly)amine after the
reaction.
[0027] The 17th embodiment of the invention is to provide a process
for producing a grease composition for a hard disk drive as
described in any of the 11th to 16th embodiment, wherein the
residual amount of the starting material is 30 ppm or less.
[0028] According to claim the invention, a grease composition for
EDD of which the outgas level is very low can be realized.
Moreover, the polyurea contained in the basal oil exists as very
fine particles and is very effective in an increase of an acoustic
lifetime.
[0029] The grease composition for a hard disk drive of the
invention contains a basal oil comprising a paraffin-base
hydrocarbon and a polyurea as a thickener.
[0030] The paraffin-base hydrocarbon is used as basal oil because
it is more stable and less in a volatile component than, for
example, ester-type basal oils. In view of this point, it is
preferred to use a synthetic paraffin-base hydrocarbon, in which
the main component is preferably those of which the carbon number
is 30 or more and contains substantially no volatile component of
which the carbon number is less than 30. The volatile component of
which the carbon number is less than 30 may preferably be contained
at a content of 30 ppm or less. This volatile component may be
eliminated in advance or in the course of the production.
[0031] In a preferred embodiment, it is preferable to use a
polyolefin represented by the above-mentioned formula 1 alone or as
a mixture. Such a polyolefin is available as SHINFIELD PAO (trade
name) (made by Nippon Steel Chemical Co. Ltd.) or PAO SH series
(trade name)(made by Exxon-Mobil Corp.).
[0032] The content of the polyurea in the grease composition for
HDD of the invention is usually in 2-50 weight parts for 100 weight
parts of basal oil, at which content the basal oil can be
thickened.
[0033] The polyurea may be prepared by adding a starting
poly-isocyanate and a primary or secondary amine or polyamine
(herein the amine or polyamine is referred to as (poly)amine) to a
basal oil, in which reaction it is preferable to use a
polyisocyanate readily soluble in the paraffin-base hydrocarbon.
The reason is that when the polyisocyanate exists as large
particles incompatible with the basal oil the generated polyurea is
not of fine particles and poor in acoustic properties.
[0034] In this invention, the polyurea is preferably contained in
an average particle size of 1 im or less, because particles larger
than this size results in an insufficient acoustic property.
[0035] In this connection, it is preferable to use an aliphatic
polyisocyanate as readily soluble in the paraffin-base hydrocarbon,
including, for example, 1, 6-hexane diisocyanater isophorone
diisocyanate, hydrogenated diphenylmethane diisocyanate, and the
like. In addition, metaxylylene diisocyanate that is readily
soluble in paraffin-base hydrocarbons may preferably be used though
it is aromatic. Thus, the polyisocyanate can be dissolved
compatibly as fine particles in a paraffin-base hydrocarbon, in
which the (poly) amine added is allowed to react to yield the
polyurea as fine particles. In this operation, it is necessary to
select a stirring condition in order to give a compatible
solubility as fine particles to the polyisocyanate.
[0036] In the reaction of the starting polyisocyanate and the
primary or secondary (poly)amine added to the basal oil to yield
the polyurea, it is preferable to add an excess amount of the
(poly)amine to the polyisocyanate since the (poly)amine can more
easily be removed among the starting materials remaining unchanged.
In this respect, the (poly) amine is preferably used in a molecular
weight as small as possible, preferably, of 400 or less.
[0037] Accordingly, it is preferable to add the polyisocyanate and
the (poly) amine to the basal oil to yield the polyurea and then
treat the latter under reduced pressure.
[0038] Thus, the starting materials remaining unchange regarded as
the cause of outgas can be removed so that the content of the
starting materials is preferably 30 ppm or less.
[0039] In this operation, the treatment under reduced pressure may
preferably be carried out in such a condition as at least the
starting materials for the polyurea can be removed, for example, at
a degree of 300 mmHg or lower, preferably, 10 mmHg or lower. The
treatment under reduced pressure may be performed at a temperature
of 50-200.degree. C., preferably 100-150.degree. C., for a period
of 30 minutes or longer, preferably 2 hours or longer.
[0040] The treatment under reduced pressure may be achieved with a
vacuum pump or water-jet pump, as well as with molecular
distillation, azeotropic distillation, etc.
[0041] By such treatment, the starting materials remaining
unchanged and the volatile components in the basal oil are removed
and very low outgas-level grease can be realized.
[0042] In this connection, the treatment under reduced pressure may
be effected not only after the reaction completion but also on the
basal oil alone. Thus, low molecular weight components can be
removed even in the basal oil containing low molecular components.
Accordingly, the components of which the carbon number is less than
30 are preferably reduced, for example, to a content of 30 ppm or
less, more preferably so that they contain substantially no low
molecular weight component.
[0043] The grease compositions of the invention may contain further
additives for improving other grease properties as far as they
afford decisive effect on the generation of outgas. Such additives
include antioxidants, lubrication enhancers, rust preventives,
thickeners, surfactants, and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 depicts a diagrammatic section view of a hard disk
drive.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] The invention is illustrated in more detail according to
claim the following examples.
EXAMPLE 1
[0046] In a 100 ml flask equipped with a stirrer was placed 50 g of
a paraffin-base hydrocarbon as basal oil, PA0401 (trade name;
Nippon Steel Chemical Co., Ltd.), to which were added 5 g of liquid
polyisoprene rubber, LIR-290 (trade name; Kuraray Co., Ltd.), and
3.0 g of isophorone diisocyanate. After stirring, 2.0 g of
n-butylamine was dropwise added, and the mixture was allowed to
react at 30.degree. C. for 1 hour to yield polyurea (polyurea
content: 10 weight %). Thereafter, the mixture was kept under
reduced pressure of 1 mmHg at 100.degree. C. for 60 minutes to
yield grease for HDD.
EXAMPLE 2
[0047] In a 200 ml flask equipped with a stirrer was placed 100 g
of a paraffin-base hydrocarbon, PA0401 (trade name; Nippon Steel
Chemical Co., Ltd.) as basal oil, to which were added 4 g of a
methacrylic polymer, KANELUBE 815 (trade name; Kanebo Chemical
Industires, Ltd.), and 6.65 g of 1,6-hexane duisocyanate. After
stirring, 13.35 g of n-dioctylamine was dropwise added, and the
mixture was allowed to react at 50.degree. C. for 2 hours to yield
polyurea (polyurea content: 20 weight %) Thereafter, the mixture
was kept under reduced pressure of 10 mmHg at 120.degree. C. for
240 minutes to yield grease for HDD.
EXAMPLE 3
[0048] In a 100 ml flask equipped with a stirrer was placed 50 g of
a paraffin-base hydrocarbon as basal oil, PA0601 (trade name;
Nippon Steel Chemical Co., Ltd.), to which were added 17 g of a
polyolefin polyol, EPOL (trade name; Atofina Idemitsu Co., Ltd.),
and 4.50 g of hydrogenated diphenylmethane diisocyanate. After
stirring, 3.00 g of cyclohexylamine was dropwise added, and the
mixture was allowed to react at 15.degree. C. for 1 hour to yield
polyurea (polyurea content: 15 weight %). Thereafter, the mixture
was kept under reduced pressure of 160 mmHg at 150.degree. C. for
480 minutes to yield grease for HDD.
EXAMPLE 4
[0049] Decene tetramer as basal oil was provided by molecular
distillation of a polyolefin, PAO801 (trade name; Nippon Steel
Chemical Co., Ltd.). This decenetetramer (carbon number:40)(3 g)
was placed in a glass petri dish and the outgas generated at
85.degree. C. for 3hours was measured by means of GC-MS. The
volatile components of which the carbon number was less than 30 was
contained at a level of 15 ppm.
[0050] In a 200 ml flask equipped with a stirrer was placed 100 g
of this decene tetramer, to which were added 10 g of liquid
polybutadiene, LIR-30 (tradename; Kuraray Co., Ltd.), and 7.95 g of
1,6-hexane diisocyanate. After stirring, 0.93 g of ethylene diamine
and 6.12 g of laurylamine were dropwise added, and the mixture was
allowed to react at 50.degree. C. for 1 hour to yield polyurea
(polyurea content: 15 weight %). Thereafter, the mixture was kept
under reduced pressure of 50 mmHg at 80.degree. C. for 120 minutes
to yield grease for HDD.
Comparative Example 1
[0051] To an alkyl-substituted diphenyl ether (ADE) (trade name;
MORESCO-HILUBE LS150) as basal oil were added toluene diisocyanate
and n-butylamine to yield diurea as grease (diurea content: 20
weight %).
Comparative Example 2
[0052] To a paraffin-base hydrocarbon, PA0401 (trade name; Nippon
Steel Chemical Co., Ltd.) as basal oil, was added 20 weight % of
lithium soap (lithium stearate) as thickener to yield grease.
Comparative Example 3
[0053] To an ester oil (medium fatty acid ester) as basal oil was
added 20 weight % of lithium soap (lithium stearate) as thickener
to yield grease.
Comparative Example 4
[0054] Commercially available NIGACE (trade name; made by Nippon
Grease Co., Ltd.) was used as grease.
Comparative Example 5
[0055] Commercially available ASONIC GHY72 (trade name; made by
Kluber Lubrication Munchen KG.) was used as grease.
Test Example 1
Determination of Outgas
[0056] Grease obtained respectively in Examples and Comparative
Examples was put on the pivot bearings in an amount of 3.1 mg each,
and the bearings were baked in an oven at 85.degree. C. for 3
hours. The gas generated by this operation was measured by means of
AGC-MS.
[0057] As GC-MS, a gas chromatography mass selection detector was
used.
[0058] Table 1 shows the results. The amount of outgas (ng/pcs)
indicates the gas weight (ng) per pivot bearing.
1 TABLE 1 Amount of Outgas (ng/pcs) Example 1 1220 Example 2 830
Example 3 1610 Example 4 980 Comparative Example 1 34200
Comparative Example 2 29900 Comparative Example 3 44000 Comparative
Example 4 26500 Comparative Example 5 15800
Test Example 2
Acoustic Test (Anderon Test)
[0059] Grease obtained respectively in Examples and Comparative
Examples was put on the pivot bearings. The inner ring was rotated
at 1800 rpm, and a probe was made touch to the outer ring. The
resulting vibration was measured with a measuring apparatus,
ANDERON, at the following 3 bands.
[0060] LOW: 50-300Hz, MID.: 300-1800Hz, HIGH: 1800Hz-10kHz
2 TABLE 2 LOW MID HIGH Example 1 2.6 0.6 0.7 Example 2 2.7 0.8 0.6
Example 3 2.6 0.6 0.8 Example 4 2.6 0.7 0.9 Comparative Example 1
4.2 1.5 2.1 Comparative Example 2 4.5 1.4 2.5 Comparative Example 3
4.4 1.8 2.8 Comparative Example 4 2.8 0.8 0.9 Comparative Example 5
2.8 0.8 1.0
[0061] From the above results it was found that the grease in
Examples 1-4 has the same characteristics as or better than the
commercially available grease shown in Comparative Examples 4 and
5.
Test Example 3
Torque Test
[0062] Grease obtained respectively in Examples and Comparative
Examples was put on the pivot bearings. To two inner rings of the
pivot bearings of size 614 was given 600 grf of preload, and the
shaft (inner ring side) was rotated at 2 rpm. A gauge was applied
to the sleeve (outer ring side) to measure rotatory torque. Table 3
shows the results.
3 TABLE 3 Running Torque Peak to Peak g .multidot. cm g .multidot.
cm Example 1 1.0 0.3 Example 2 1.0 0.3 Example 3 1.0 0.3 Example 4
0.9 0.3 Comparative Example 1 1.2 0.4 Comparative Example 2 1.3 0.3
Comparative Example 3 1.2 0.4 Comparative Example 4 1.1 0.4
Comparative Example 5 1.0 0.3
[0063] As results, it was found that any of grease has
approximately the same performance.
Test Example 4
Life Test
[0064] Grease obtained respectively in Examples and Comparative
Examples was put on the pivot bearings. These pivot bearings were
subjected to the life test in the following condition, and it was
confirmed that there was no difference between the torque checked
before the test and that after the test.
Condition
[0065] Speed: 15Hz
[0066] oscillating angle: 300
[0067] Time: 38,000,000 revolutions
[0068] As results, it was found that any of grease maintained
faultless performance in view of the lifetime.
[0069] As described above, according to claim the invention, it is
possible to provide the most appropriate grease for HDD of which
outgas is very low, which is prepared by making a thickener
polyurea contain in basal oil comprising a given paraffin-base
hydrocarbon, followed by treatment under reduced pressure.
* * * * *